<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<button id="btn01">点我一下</button>
<script>
    window.onload = function () {
        var btn01 = document.getElementById('btn01');
        btn01.onclick = ()=>{
            alert(this);
        };
    };



</script>

</body>
</html>